Abstract
Elimination of sensory inputs (deprivation) modifies the properties of the sensory cortex and serves as a model for studying plasticity during postnatal development. Many studies on the effects of deprivation have been performed in the visual cortex using dark-rearing as a visual deprivation model. It induces changes in all cellular and molecular components, including astrocytes, which play an important role in the development, maintenance, and plasticity of the cortex, mediated by cytokines which have been termed angioglioneurins. When one sense is deprived, a compensatory mechanism called cross-modal plasticity increases performance in the remaining senses. Environmental enrichment is so far the best-known method to compensate sensorial deprivation. The aim of this work is to study the effects of exercise alone, and of an enriched environment combined with exercise, on astroglial population in order to observe the effects of exercise by itself, or the potential synergistic effect during the rat visual system development. Pregnant Sprague-Dawley rats were raised in one of the following rearing conditions: in total darkness and enriched environment conditions with physical exercise, and in total darkness with voluntary physical exercise. Astrocytic density was estimated by immunohistochemistry for S-100β protein and quantifications were performed in layer IV. The somatosensorial cortex barrel field was also studied as control. Our main result shows that an enriched environment combined with voluntary physical exercise manages to reverse the negative effects induced by darkness over the astroglial population of both the visual and the somatosensory cortices. On the other hand, exercise alone only produces effects upon the astroglial population of the somatosensory cortex, and less so when combined with an enriched environment.
Highlights
In most species sensory systems are immature at birth and their postnatal development is refined by sensory inputs which induce changes at behavioral, functional, cellular, and molecular levels (Greenough et al, 1987; Bengoetxea et al, 2012; Levelt and Hübener, 2012)
Immunoreactivity for S-100β was similar at all different ages both in the primary visual cortex and the primary somatosensory cortex, where strongly stained cell bodies and star-shaped processes were found across all cortical layers
The density of S-100β cells per area in the layer IV of the visual cortex was higher in the DR-EE-Ex group during the development with differences of 96% at P21 (11.70 ± 0.35 and 22.95 ± 0.59, Dark rearing with exercise (DR-Ex) vs. DR-EE-Ex), 30% at P28 (15.18 ± 0.37 and 19.60 ± 0.43), 64% at P35 (12.03 ± 0.33 and 19.72 ± 0.47), 68% at P42 (11.64 ± 0.28 and 19.56 ± 0.47), 90% at P49 (10.79 ± 0.33 and 20.51 ± 0.68), 54% at P56 (11.99 ± 0.38 and 18.46 ± 0.73) and 77% at P63 (11.06 ± 0.33 and 19.55 ± 0.49)
Summary
In most species sensory systems are immature at birth and their postnatal development is refined by sensory inputs which induce changes at behavioral, functional, cellular, and molecular levels (Greenough et al, 1987; Bengoetxea et al, 2012; Levelt and Hübener, 2012). Changes reach their maximum during the critical period (Hensch, 2004, 2005), a time window specific for each sensorial cortex. These molecules include factors initially described as neurotrophic factors, such as the brain derived neurotrophic factor (BDNF); angiogenic factors, such as the vascular endothelial growth factor (VEGF); or metabolic factors, such as the insulin-like growth factor (IGF) or erythropoietin (EPO; Zacchigna et al, 2008)
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